With the rising of communication service volume and miniaturization of communications devices, the mainstream Serdes signal rate has been raised to 10.3125 Gbps, 12.5 Gbps, or even directly up to 25 Gbps in the next step; as the signal rate is greatly improved, stricter requirements are placed the quality of differential signals, especially the control of pin skew.
In addition to the differences between physical sizes of PCB wires, the glass fiber weave effect of glass fiber fabrics is a more important reason which causes differential signal skew. Because glass fiber fabrics are formed by bonding and laminating glass fiber with epoxy resin, and the relative dielectric constants at various positions are different due to glass fiber warps and wefts, different heights of glass fiber at weaving spacing and varying contents of epoxy resin. After a PCB routes wires (or wires are formed on the PCB), two differential signal lines land on glass fiber fabrics at random, thereby resulting in the pin skew.
Existing methods for controlling differential signal skew mainly include: rotating glass fiber fabrics during processes, tilting all wires as a whole (to make the wires and the glass fiber warps and wefts form acute angles), or a zig-zag routing approach.
At present, the commonly used approaches of rotating glass fiber fabrics, tilting all wires as a whole and zig-zag routing have defects in costs control and wiring space, and these defects impose more influences on backplanes of large size. Existing methods for controlling the differential line skew have at least the following problems.
1. In the approach of rotating glass fiber fabrics during process, the glass fiber fabrics need to be tailed, thereby resulting in wastes of materials and increase of costs. Particularly, if the approach is applied on large backplanes, more wastes of board materials and further increase of costs will occur.
2. in the zig-zag routing approach (or the zig-zag wiring approach), wires need to be adjusted by small angles for a number of times, thereby resulting in irregular layout, occupation of relatively large wiring space, increased difficulties in wiring and long design cycle. The zig-zag routing approach is suitable for sub-card (daughter card) wiring, and if the approach is applied on backplanes, more wiring space will be occupied.
3. in the approach of tilting all wires as a whole, wiring becomes more difficult, and more wiring time is needed.
This section provides background information related to the present disclosure which is not necessarily prior art.